1. Field of the Invention
This invention relates generally to electronic dial combination locks having improved tamper resistance, and more specifically to such locks wherein a locking mechanism is opened by rotation of the dial.
2. Description of the Related Art
Electronic dial combination locks allow authorized personnel to access otherwise inaccessible security regions such as safes, lock boxes, storage rooms and the like. One such class of lock is the electronic dial combination lock which uses a dial having divisions to enter a combination code to gain entrance to the secured area. The lock has a spindle journaled within the lock for both rotational and axial movement to cause a push pin located on an internal cam wheel to engage one of a plurality of pressure-sensitive switches within the lock located in an evenly-spaced circular pattern centered on the shaft's axis, each switch being capable of making a discrete, unique electrical connection. A circuit contained in the secured region senses the electrical connections and detects when a given subset of connections has been made corresponding to the lock's combination and initiates an electrical signal within the secured region. The signal may be used, e.g., to operate a solenoid to permit a conventional fence lever to engage the cam wheel such that a bolt within the lock may be withdrawn, such as in a safe door. Such a lock is shown and described in U.S. Pat. No. 4,745,784. In the lock of that patent, when the correct combination is entered, the solenoid releases a fence lever so that a nose part formed thereon falls by gravity onto the circumferential surface of a cam wheel. The cam wheel is rotated by the combination dial until the nose part on the fence lever engages the slot in the circumference of the cam wheel to allow withdrawal of the bolt in the locking mechanism.
It has been recognized heretofore that it would be desirable to have a positive drive of the fence toward the tumbler wheel gates and the lever nose toward its cam wheel slot to ensure operation of the lever on entry of the combination. Generally these locks have employed a cam mechanism operated off of dial rotation to drive its fence lever toward the wheel once on each rotation of the dial. Such a lock is illustrated in U.S. Pat. No. 4,910,981. However, there is the possibility of learning something about the lock's internal parts from such regular impacting of the wheel by its fence or unauthorized manipulation of the lock by lock experts.
There is thus a need for a dial combination lock which does not allow an unauthorized user to obtain information about the characteristics of the gate tumbler wheels or the slotted cam wheel through manipulation of the combination dial and fence lever. Additionally, there is a need for a combination lock which prevents engagement of the fence lever with the tumbler wheels or the cam wheel until such time as the correct combination has been dialed into the lock mechanism and the nose part on the lever is aligned with the slot on the cam wheel. There is also a need for a combination lock which provides for positive movement of the lever into engagement with the slot in the cam wheel upon alignment through rotation of the combination dial.